Data transmission method and apparatus in network supporting coordinated transmission

ABSTRACT

A data transmission method and an apparatus in a network supporting coordinated multipoint transmission are provided. The method includes transmitting candidate sets of initial state information used to generate Demodulation Reference Signal (DMRS) scrambling sequences for the transmission points to the UE, and transmitting an indication corresponding to at least one candidate set of initial state information respectively associated with at least one transmission point to the UE, wherein the initial state information is used by the UE to generate DMRS scrambling sequences.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of a U.S.Provisional application filed on Feb. 7, 2012 in the U.S. Patent andTrademark Office and assigned Ser. No. 61/596,019, and a U.S.Provisional application filed on Feb. 9, 2012 in the U.S. Patent andTrademark Office and assigned Ser. No. 61/597,139, the entire disclosureof which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for datatransmission in a network supporting coordinated transmission. Moreparticularly, the present invention relates to a data transmissionmethod and apparatus wherein, in order to send data to a User Equipment(UE) through multiple transmission points, a base station sendsinformation used to generate a Demodulation Reference Signal (DMRS)scrambling sequence and the UE generates the DMRS scrambling sequenceusing the received information.

2. Description of the Related Art

In contrast to related-art mobile communication systems that may provideonly voice-oriented services, advanced mobile communication systems mayprovide high-quality data and multimedia services using high-speedpacket data communication. In recent years, in order to supporthigh-speed and high-quality packet data transmission services, variousmobile communication standards, such as High Speed Downlink PacketAccess (HSDPA), High Speed Uplink Packet Access (HSUPA), Long TermEvolution (LTE), Long Term Evolution Advanced (LTE-A), developed by the3^(rd) Generation Partnership Project (3GPP), High Rate Packet Data(HRPD), developed by the 3GPP 2 (3GPP2), and Institute of Electrical andElectronics Engineers (IEEE) 802.16, have been developed.

In particular, the LTE system has been developed so as to efficientlysupport high-speed wireless packet data transmission and also attemptsto maximize wireless system throughput using various radio accesstechnologies. LTE-A is an advanced version of LTE with increased datarates. Existing 3^(rd) Generation (3G) packet data communicationsystems, such as HSDPA, HSUPA and HRPD employ Adaptive Modulation andCoding (AMC) and channel-aware scheduling in order to enhancetransmission efficiency.

A transmitter using AMC may adjust an amount of transmission dataaccording to channel state. That is, when channel conditions are notgood, the amount of transmission data may be reduced so as to maintain adesired error rate at the receiver, and when channel conditions arefavorable, the amount of transmission data may be increased for higherefficiency while maintaining a desired error rate at the receiver.

The transmitter using channel-aware scheduling for resource managementmay selectively serve a specific user, from among many users, with themost favorable channel conditions. Hence, system throughput may beincreased in comparison to a case in which channel resources areallocated to one user. This effect is referred to as multi-userdiversity gain. In other words, the transmitter employing AMC andchannel-aware scheduling receives partial channel state information asfeedback from receivers and applies appropriate modulation and codingschemes in a timely manner.

When AMC is used together with Multiple Input Multiple Output (MIMO)transmission, AMC may also be used to determine a number, or rank, ofspatial layers, which may also be referred to as transmission layers,for signal transmission. In this case, in addition to the coding rateand modulation scheme, the number of transmission layers to be used maybe considered in order to determine an optimal data rate.

Recently, Code Division Multiple Access (CDMA) used in 2^(nd) Generation(2G) and 3G mobile communication systems is being merged into OrthogonalFrequency Division Multiple Access (OFDMA) in next generation mobilecommunication systems. As OFDMA is expected to increase systemthroughput beyond CDMA, systems developed by the 3GPP and 3GPP2 haveinitiated standardization of evolved systems based on OFDMA. Increasedsystem throughput using OFDMA may be achieved by using frequency domainscheduling. As channel-aware scheduling considers channel conditionsvarying with time in order to increase system throughput, considerationof channel conditions varying with frequency may contribute to furtherenhancement of system throughput.

FIG. 1 illustrates a cellular system having multiple cells according tothe related art.

Referring to FIG. 1, a cellular system may provide mobile communicationservices using various schemes described above. More specifically, inthe mobile communication system having three cells, Cell 0 through Cell2 shown in FIG. 1, an antenna for transmission and reception isinstalled in each cell. A Base Station (BS), such as an enhanced Node B(eNB), may be placed at each of cells Cell 0, Cell 1 and Cell 2, inorder to send data to User Equipments (UEs within the correspondingcell.

A UE 0 within a service area of Cell 0 receives a data signal 100 fromthe eNB of Cell 0. Similarly, eNBs of Cell 1 and Cell 2 respectivelysend data signals 110 and 120 to UE 1 and UE 2 using the sametime-frequency resources. Respective transmissions from Cell 0, Cell 1and Cell 2 to UE 0, UE 1 and UE 2 correspond to non-CoordinatedMultiPoint (non-CoMP) transmission, wherein radio resources of one cellare used only for UEs within the cell.

In FIG. 1, a UE within a cell may know an available time-frequencyresource from among signals sent by the corresponding eNB in advance.For example, UE 0 may determine a location of a Cell-specific ReferenceSignal (CRS) and a number of OFDM symbols on a control channel in atime-frequency grid 130 formed by Cell 0 before reception of a PhysicalDownlink Shared Channel (PDSCH).

As shown in FIG. 1, PDSCH resources allocated to UE 0, UE 1 and UE 2 aredifferent in the time-frequency grids 130, 140 and 150 formedrespectively by Cell 0, Cell 1 and Cell 2. When non-CoMP transmission isused, a UE receives a signal from a fixed cell. For example, in FIG. 1,UE 0 receives a signal only from Cell 0, unless it is handed over toanother cell through separate higher layer signaling.

In the time domain, an LTE and/or LTE-A downlink transmission, as shownin FIG. 1, may be split into a control region and a data region. Thecontrol region may be used to transmit control channels, such as aPhysical Downlink Control Channel (PDCCH), a Physical HARQ IndicatorChannel (PHICH), and a Physical Control Format Indicator Channel(PCFICH). In a subframe, the control region may correspond to one, twoor three OFDM symbols from the beginning

The data region may start at an OFDM symbol that is disposed immediatelyafter the control region, and may be used for a PDSCH transmission.Because a subframe is composed of fixed number of OFDM symbols, the dataregion size may be determined by the control region size. In the LTEand/or LTE-A system, a UE may refer to control information carried bythe PCFICH in order to know the control region size and in order todetermine the data region size accordingly.

In FIG. 1, a signal sent by one cell may interfere with a signal sent byanother cell, and accordingly, randomization of interference may enhancesignal reception performance. For example, when signals are respectivelysent from Cell 0 and Cell 1 to UE 0 and UE 1 through the same radioresources, the signals may interfere with each other. Thus, it isdesirable to randomize interference for better reception performance.For this reason, in the LTE and/or LTE-A system, different scramblingsequences are applied to DeModulation Reference Signals (DMRS) sent bydifferent cells. In order to achieve this, scrambling sequencegenerators of different cells have different initial states, becausescrambling sequence generators with different initial states generatedifferent scrambling sequences. That is, when cells apply differentlyinitialized scrambling sequences, inter-cell interference may beeffectively randomized.

In contrast to non-CoMP transmission, CoMP transmission enables multiplebase stations to send signals to one UE. When CoMP transmission is used,one UE may receive signals from multiple base stations. Hence, it ispossible to provide an improved data rate to a UE far from a basestation. Similarly to the case of non-CoMP transmission, in order torandomize interference between signals from multiple base stationsparticipating in CoMP transmission, the multiple base stations shouldapply different scrambling sequences.

Therefore, a need exists for a system and method for multiple basestations to apply different scrambling sequences for CoMP transmissions.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a method and apparatus that determine initialstates for Demodulation Reference Signal (DMRS) scrambling so as torealize effective Coordinated Multipoint (CoMP) transmission and/orreception in a Long Term Evolution (LTE) and/or LTE-Advance (LTE-A)system.

In accordance with an aspect of the present invention, a datatransmission method for a Base Station (BS) capable of sending data to aUser Equipment (UE) through multiple transmission points is provided.The method includes transmitting candidate sets of initial stateinformation used to generate DMRS scrambling sequences for thetransmission points to the UE, and transmitting an indicationcorresponding to at least one candidate set of initial state informationrespectively associated with at least one transmission point to the UE,wherein the initial state information is used by the UE to generate DMRSscrambling sequences.

In accordance with another aspect of the present invention a datareception method for a UE capable of receiving data from a BS throughmultiple transmission points is provided. The method includes receiving,from the BS, candidate sets of initial state information used togenerate DMRS scrambling sequences for the multiple transmission points,receiving, from the BS, an indication corresponding to a candidate setof initial state information associated with a transmission pointdetermined in order to generate the DMRS scrambling sequences,determining an initial state for generating the DMRS scramblingsequences according to the indicated candidate set of initial stateinformation, and generating the DMRS scrambling sequences according tothe determined initial state.

In accordance with another aspect of the present invention, a datatransmission apparatus acting as a base station is provided. Theapparatus includes a wireless communication unit for sending data to aUE through multiple transmission points, and a control unit forcontrolling a process of transmitting, to the UE, candidate sets ofinitial state information used to generate DMRS scrambling sequences forthe transmission points, and for transmitting an indicationcorresponding to at least one candidate set of initial state informationrespectively associated with at least one transmission point to the UE,wherein the initial state information is used by the UE to generate theDMRS scrambling sequences.

In accordance with another aspect of the present invention, a datareception apparatus acting as a UE is provided. The apparatus includes awireless communication unit for receiving data from a BS throughmultiple transmission points, a control unit for controlling a processof receiving, from the BS, candidate sets of initial state informationused to generate DMRS scrambling sequences for the multiple transmissionpoints, and for receiving, from the BS, an indication corresponding to acandidate set of initial state information associated with atransmission point determined in order to generate the DMRS scramblingsequences, and a sequence generation unit for determining an initialstate for generating the DMRS scrambling sequences according to theindicated candidate set of initial state information, and for generatingthe DMRS scrambling sequences according to the determined initial state.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates a cellular system having multiple cells according tothe related art;

FIG. 2 illustrates a Long Term Evolution (LTE) and/or LTE-Advanced(LTE-A) multi-cell system supporting Dynamic Point Selection (DPS) inwhich a User Equipment (UE) receives a Physical Downlink Shared Channel(PDSCH) and a Demodulation Reference Signal (DMRS) from one of at leastthree different cells according to an exemplary embodiment of thepresent invention;

FIGS. 3A and 3B illustrate Multi User-Multi Input Multi Output (MU-MIMO)transmission in a multi-cell network supporting Coordinated Multi Point(CoMP) operation according to an exemplary embodiment of the presentinvention;

FIG. 4 is a flowchart of a procedure to determine an initial state forDMRS scrambling according to an exemplary embodiment of the presentinvention;

FIG. 5 illustrates an information field indicating a set of three piecesof information for scrambling sequences, which is notified by anenhanced Node B (eNB) to a UE through a Physical Downlink ControlChannel (PDCCH) or an Enhanced-PDCCH (E-PDCCH) according to an exemplaryembodiment of the present invention;

FIG. 6 illustrates an information field indicating a set of CellIdentification (ID) and subframe offset values and another informationfield indicating an n Scrambling Identification (n_(SCID)) value, amongthree pieces of information for scrambling sequences, which are notifiedby an eNB to a UE through a PDCCH or an E-PDCCH according to anexemplary embodiment of the present invention;

FIG. 7 is a flowchart of an eNB procedure to determine an initial statefor DMRS scrambling according to an exemplary embodiment of the presentinvention;

FIG. 8 illustrates an information field indicating a set of two piecesof information for scrambling sequences, which is notified by an eNB toa UE through a PDCCH or an E-PDCCH according to an exemplary embodimentof the present invention;

FIG. 9 illustrates an information field indicating a Cell ID and anotherinformation field indicating an n Scrambling Identification (n_(SCID))value, among two pieces of information for scrambling sequences, whichare sent by an eNB to a UE through a PDCCH or an E-PDCCH according to anexemplary embodiment of the present invention;

FIG. 10 is a flowchart of a UE procedure to generate DMRS scramblingsequences according to the second exemplary embodiment of the presentinvention;

FIG. 11 is a flowchart for determining a subframe offset using receivedCell ID in the procedure of FIG. 10 according to an exemplary embodimentof the present invention;

FIG. 12 is a block diagram of a data transmission apparatus according toan exemplary embodiment of the present invention; and

FIG. 13 is a block diagram of a data reception apparatus according to anexemplary embodiment of the present invention.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

Detailed Description of Exemplary Embodiments

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

The exemplary embodiments are described below with respect to a wirelesscommunication system based on Orthogonal Frequency Division Multiplexing(OFDM), in particular, with respect to the 3^(rd) Generation PartnershipProject (3GPP) Evolved Universal Terrestrial Radio Access (EUTRA)standards. However, the present invention is not limited thereto, andfeatures described below with respect to the exemplary embodiments areapplicable to other communication systems having similar technicalbackgrounds and channel structures without much modification.

For interference randomization, a User Equipment (UE) determines aninitial state for DMRS scrambling according to Equation 1.

c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +n _(SCID)   [Equation1]

In Equation 1, n_(s) is a slot number in a current radio frame, n_(cell)^(ID) is a Cell ID of a cell to which the UE is connected after handoveror initial access, and n Scrambling Identification (n_(SCID)) is ascrambling index. Here, information needed to determine the initialstate for DMRS scrambling, such as a slot number, the Cell ID, and thescrambling index, is referred to as initial state information. The UEmay identify the Cell ID N_(cell) ^(ID) from a synchronization signalfrom the current cell. Alternatively, a Base Station (BS) may notify theCell ID to the UE through higher layer signaling. In the presentexemplary embodiment, the Cell ID that is notified through higher layersignaling is a virtual cell ID other than a physical Cell ID. However,the present invention is not limited thereto, and a physical cell ID ora virtual cell ID may be the Cell ID. The value of n_(SCID) may be 0 or1, and n_(SCID) is notified by the network to the UE through a controlchannel PDCCH or E-PDCCH.

In addition, n_(s) refers to a slot number in the current radio frame.In the LTE and/or LTE-A system, a time domain may be subdivided intoradio frames, and each radio frame may have an interval of 10 ms. Oneradio frame is composed of ten subframes, and each subframe may have aninterval of 1 ms. One subframe is split into two slots, and each slothas an interval of 0.5 ms. That is, one radio frame is composed of 20slots, and the slot number identifies a specific slot, from among the 20slots, in the radio frame. The UE may identify the beginning of a radioframe through time and frequency synchronization using a synchronizationsignal and may determine the slot number of a particular slot.

In order to avoid collision between synchronization signals, differentcells may apply time differences. In the present exemplary embodiment,different cells may be associated with different slot numbers in thesame time interval. This time difference may be referred to as subframeoffset, and subframe offsets may be assigned to different cells in unitsof 1 ms.

In LTE and/or LTE-A Release 10, as described before, n_(SCID) isnotified to the UE through a PDCCH or an E-PDCCH. Table 1 illustrates3-bit control information that may be transmitted from the base stationto the UE to notify nl_(SCID).

TABLE 1 One Codeword: Two Codewords: Codeword 0 enabled, Codeword 0enabled, Codeword 1 disabled Codeword 1 enabled Value Message ValueMessage 0 1 layer, port 7, n_(SCID) = 0 0 2 layers, ports 7-8, n_(SCID)= 0 1 1 layer, port 7, n_(SCID) = 1 1 2 layers, ports 7-8, n_(SCID) = 12 1 layer, port 8, n_(SCID) = 0 2 3 layers, ports 7-9 3 1 layer, port 8,n_(SCID) = 1 3 4 layers, ports 7-10 4 2 layers, ports 7-8 4 5 layers,ports 7-11 5 3 layers, ports 7-9 5 6 layers, ports 7-12 6 4 layers,ports 7-10 6 7 layers, ports 7-13 7 Reserved 7 8 layers, ports 7-14

In the LTE and/or LTE-A system supporting Coordinated Multi Point (CoMP)transmission, Dynamic Point Selection (DPS) may be used for CoMPoperations. When DPS is used, transmission points, which performdownlink transmission to a given UE, may be actively changed inconsideration of radio channel states, the amount of downlink radiotraffic and a presence of other UEs, and a transmission point maycorrespond to a cell with unique Cell ID.

In the LTE and/or LTE-A system, a DMRS and a PDSCH are transmitted usinga same Resource Block (RB) in a same subframe. The UE performs channelestimation using the received DMRS and performs channel decoding for thePDSCH. In other words, the UE has to perform channel estimation usingthe received DMRS to decode data carried by the PDSCH. In a networksupporting CoMP transmission based on DSP, individual transmissionpoints may have different Cell IDs and ns values. In this case, a UEgenerates scrambling sequences by applying Cell IDs and ns valuescorresponding to the cells transmitting to the UE.

FIG. 2 illustrates an LTE and/or LTE-A multi-cell system supporting DPS,in which a UE receives a PDSCH and a DMRS from one of at least threedifferent cells.

Referring to FIG. 2, Cell 0 210 has Cell ID of X and n_(s) of P, Cell 1220 has Cell ID of Y and n_(s) of Q, and Cell 2 230 has Cell ID of Z andn_(s) of R. When different transmission points, i.e., cells, havedifferent Cell IDs and subframe offsets as in the case of the presentexemplary embodiment, then the UE 200 may be unable to determine aninitial state for the DMRS scrambling sequences using Equation 1 only.

That is, in order to determine the initial state for DMRS scramblingsequences, the UE needs to identify the Cell ID and the n_(s) valueapplied to the initial state. For example, in FIG. 2, in order toreceive the PDSCH from Cell 0, the UE 200 determines the initial stateon the basis of the Cell ID and the subframe offset used by Cell 0.Furthermore, in order to receive the PDSCH from Cell 1, the UE 200determines the initial state on the basis of the Cell ID and thesubframe offset used by Cell 1, and, in order to receive the PDSCH fromCell 2, the UE 200 determines the initial state on the basis of the CellID and the subframe offset used by Cell 2.

In a system supporting CoMP operation, an optimal combination of cellsparticipating in actual downlink transmission may be instantly changedaccording to traffic and wireless channel conditions. That is, in amobile communication system such as the LTE-A system, which performsscheduling every 1 ms, cells participating in a CoMP transmission maychange every 1 ms. As such, a network supporting CoMP operation notifiesa UE of the Cell IDs and the subframe offsets of cells currentlyparticipating in downlink transmission. This notification may beperformed by a central controller that is managing radio resources ofmultiple transmission points on a scheduling unit basis.

Notification of the Cell IDs and the subframe offsets of cellsparticipating in downlink transmission provides sufficient randomizationof interference between transmission points and, thus, supports MU-MIMOoperation. In MU-MIMO, one transmission point may send spatiallyseparated radio signals using a same time-frequency resource to multipleUEs. As an example of MU-MIMO, a transmission point may send differentpieces of data to two mobile terminals using the same time-frequencyresource on spatially separated radio signals. When MU-MIMO is used tosimultaneously send to multiple UEs, it is important to send DMRSspreserving orthogonality to the UEs. When DMRSs preserve orthogonalityin MU-MIMO transmission, a UE is free from DMRS interference with otherUEs.

For MU-MIMO operation, the LTE and/or LTE-A system provides DMRSs basedon two orthogonal codes. That is, in LTE and/or LTE-A Release 10, DMRSport 7 and DMRS port 8 are sent using the same radio resource butdifferent orthogonal codes. When a BS respectively performs a downlinktransmission of rank 1 to two UEs, the BS may preserve orthogonalitybetween DMRSs assigned to the UEs by means of DMRS port 7 and DMRS port8. In order to preserve orthogonality between DMRS ports using the sameradio resources, the same scrambling to corresponding DMRSs should beapplied. For example, when Cell 1 performs MU-MIMO operation, in orderto preserve orthogonality between DMRS ports assigned to different UEs,Cell 1 should scramble the DMRS ports in the same way.

FIGS. 3A and 3B illustrate MU-MIMO transmission in a multi-cell networksupporting CoMP operation according to an exemplary embodiment of thepresent invention.

Referring to FIGS. 3A and 3B, UE 1 310, UE 2 320 and UE 3 330 receivesignals from two cells, Cell 0 340 and Cell 1 350. Herein, UE2 320 mayreceive a PDSCH from Cell 0 340 or Cell 1 350. That is, the networksupports DPS.

In FIG. 3A, UE 2 320 receives a PDSCH from Cell 0 340. Also, UE 2 320configures an initial state in accordance with a Cell ID and a subframeoffset of Cell 0 340, and generates scrambling sequences based on theinitial state. The reason UE 2 320 configures the initial stateaccording to Cell 0 340 is to preserve orthogonality between the DMRSports respectively assigned to UE 1 310 and UE 2 320 when Cell 0 340transmits the PDSCH to UE 1 310 and UE 2 320 through MU-MIMO.

In FIG. 3B, in order to receive the PDSCH from Cell 1 350, UE 2 320configures the initial state according to the Cell ID and the subframeoffset of Cell 1 350. Similar to the exemplary embodiment of FIG. 3A, UE2 320 configures the initial state according to Cell 1 350 in order topreserve orthogonality between the DMRS ports respectively assigned toUE 2 320 and UE 3 330 when Cell 1 350 transmits the PDSCH to UE 2 320and UE 3 330 through MU-MIMO.

As described above, in order to support DPS, a UE may configure theinitial state in accordance with the Cell ID and the subframe offset ofone of multiple cells and may generate DMRS scrambling sequences basedon the initial state. Accordingly, the present exemplary embodimentsshow a scheme that notifies a UE of a Cell ID and a subframe offsetthrough PDCCH or E-PDCCH.

According to an exemplary embodiment for notifying information on theDMRS scrambling sequences to a UE, the BS may notify the UE in advanceof candidate sets of the Cell ID, the ns and the nSCID values throughhigher layer signaling and may send the UE an indication specifying oneof the candidate sets to be used in order to configure the initial statefor DMRS scrambling through PDCCH or E-PDCCH.

FIG. 4 is a flowchart of a procedure to determine an initial state forDMRS scrambling according to an exemplary embodiment of the presentinvention.

Referring to FIG. 4, a BS determines transmission points to be assignedto a UE within a coverage area thereof in step 410. That is, for CoMPoperation, the BS may determine a set of transmission points whose radioresources are to be utilized for the UE. For example, in order tosupport DPS, the BS may determine a set of cells capable of sending aPDSCH to the UE. Then, the BS notifies the UE of candidate sets of theCell ID, the n_(s) and the n_(SCID) values through higher layersignaling in step 420.

The BS sends the UE an indication specifying one of the candidate setsto be used to configure the initial state for DMRS scrambling throughthe PDCCH or the E-PDCCH in step 430. Upon reception of the indication,the UE determines an initial state for DMRS scrambling using theindicated Cell ID, n_(s) and n_(SCID) values.

Table 2 illustrates candidate sets of Cell ID, subframe offset andn_(SCID) values notified to the UE at step 420.

TABLE 2 Cell ID Subframe offset n_(SCID) Candidate Set 1 X A 0 CandidateSet 2 Y B 1

After notification of candidate sets of Cell ID, subframe offset andn_(SCID) values, as illustrated in Table 2, the BS sends an indicationto the candidate set to be used at step 430, and the UE configures theinitial state for DMRS scrambling using the indicated candidate set.According to the present exemplary embodiment, the Cell ID, subframeoffset and n_(SCID) values may be notified as a group of information, asillustrated in Table 2. However the present invention is not limitedthereto, and the BS may provide the Cell ID, subframe offset andn_(SCID) values individually to the UE.

FIG. 5 illustrates an information field indicating a set of three piecesof information for scrambling sequences, which is notified by eNB to UEthrough the PDCCH or the E-PDCCH.

Referring to FIG. 5, the BS may send an information field of one or morebits indicating a candidate set of the Cell ID, subframe offset andn_(SCID) values to the UE.

FIG. 6 illustrates an information field indicating a set of Cell ID andsubframe offset values and another information field indicating n_(SCID)value, among three pieces of information for scrambling sequences, whichare notified by an eNB to a UE through a PDCCH or an E-PDCCH.

Referring to FIG. 6, the BS may use the PDCCH or the E-PDCCH to send theUE an information field including one or more bits indicating acandidate set of the Cell ID and subframe offset values and anotherinformation field containing the n_(SCID) value and other information,such as a DMRS antenna port allocation. In another exemplary embodimentfor notifying the UE about information on the DMRS scrambling sequences,the BS may notify the UE about only the Cell ID and the n_(SCID)information, and the UE may then determine the subframe offset usingreceived Cell ID. That is, the UE receives the Cell ID and n_(SCID)values from the BS through the PDCCH or the E-PDCCH, as is the case ofthe exemplary embodiment of FIG. 4. Then, the UE identifies the subframeoffset using the received Cell ID, and determines the initial state forthe DMRS scrambling.

Hence, in present exemplary embodiment of FIG. 6, the UE autonomouslyidentifies, in advance, the Cell IDs and the subframe offsets of cellsin the vicinity of the UE. As described before, a UE may identify theCell ID and the subframe offset of a cell by receiving a synchronizationsignal from the cell. In the LTE and/or LTE-A system, a PrimarySynchronization Signal (PSS) and Secondary Synchronization Signal (SSS)are transmitted every 10 ms as a synchronization signal and may provideinformation on the Cell ID and the radio frame start point to UEs.

In the exemplary embodiment of FIG. 6, the UE identifies candidate cellscapable of sending the PDSCH thereto through the DPS and identifies theCell IDs and the subframe offsets by receiving synchronization signalsfrom the candidate cells. The candidate cells capable of participatingin the DPS operation may be identified by the UE or the BS may notifythe UE of such candidate cells. The UE may identify candidate cells bymeasuring intensity of signals from individual cells. The BS may notifythe UE of candidate cells capable of participating in DPS operationthrough higher layer signaling.

FIG. 7 is a flowchart of an eNB procedure to determine an initial statefor DMRS scrambling according to the second exemplary embodiment of thepresent invention.

Referring to FIG. 7, the BS determines candidate transmission points orcells capable of participating in DPS operation for a UE in step 710.Next, the BS notifies the UE of the Cell IDs and n_(SCID) values of thecandidate transmission points or notifies the UE of the cells determinedat step 710 through higher layer signaling in step 720.

The BS notifies the UE of the Cell ID and the nSCID value to be used inorder to determine the initial state for DMRS scrambling through thePDCCH or the E-PDCCH in step 730. Similar to the exemplary embodiment ofFIG. 4, for one candidate cell, the BS may notify the UE of the Cell IDand the n_(SCID) value as a group of information or may notify the UE ofthe Cell ID and the n_(SCID) value separately.

FIG. 8 illustrates an information field indicating a set of two piecesof information for scrambling sequences, which is notified by the eNB tothe UE through the PDCCH or the E-PDCCH according to an exemplaryembodiment of the present invention.

Referring to FIG. 8, the BS, which may be the eNB, may send aninformation field, including one or more bits indicating a candidate setof the Cell ID and n_(SCID) value, and other information to the UE.

FIG. 9 illustrates an information field indicating the Cell ID andanother information field indicating the n_(SCID) value, among twopieces of information for scrambling sequences, which are sent by eNB toUE through the PDCCH or the E-PDCCH according to an exemplary embodimentof the present invention.

Referring to FIG. 9, the stations, which may be the eNB, may use thePDCCH or the E-PDCCH to send the UE an information field including oneor more bits indicating the Cell ID and another information fieldcontaining the n_(SCID) value and other information, such as DMRSantenna port allocation. After the reception of the Cell ID and then_(SCID) value, the UE may determine a subframe offset of acorresponding cell using the received Cell ID and n_(SCID) value, andmay generate the DMRS scrambling sequences using the subframe offset.

FIG. 10 is a flowchart of a UE procedure to generate the DMRS scramblingsequences according to the second exemplary embodiment of the presentinvention.

Referring to FIG. 10, the UE receives candidate Cell IDs and n_(SCID)values from a BS through higher layer signaling in step 1010. Asdescribed above, the candidate Cell ID and the n_(SCID) value may bereceived as a candidate set, i.e. as a group, or may be separatelyreceived. The UE receives an indication of the Cell ID and the n_(SCID)value to be used to generate the DMRS scrambling sequences from the BSthrough the PDCCH or the E-PDCCH in step 1020. The indication of theCell ID and the n_(SCID) value may be transmitted using an informationfield described with reference to FIGS. 8 and 9.

The UE determines a subframe offset in accordance with the indicatedCell ID in step 1030. As described before, the UE identifies, inadvance, the Cell IDs and the subframe offsets of cells in the vicinityof the UE. The UE determines the initial state for the DMRS scramblingusing the notified Cell ID and the n_(SCID) value and using thedetermined subframe offset, and then generates the DMRS scramblingsequences in step 1040.

FIG. 11 is a detailed flowchart for determining a subframe offset usinga received Cell ID in the procedure of FIG. 10 according to an exemplaryembodiment of the present invention.

Referring to FIG. 11, the UE determines whether the Cell ID receivedfrom the BS belongs to a set of candidate Cell IDs that have beenreported to the BS as a result of a Reference Signal Received Power(RSRP) measurement in step 1110. If it is determine, in step 1110, thatthe received Cell ID belongs to the set of reported candidate Cell IDs,then the UE determines to use a subframe offset corresponding to thereceived Cell ID for the DMRS scrambling in step 1120. In contrast, whenthe received Cell ID does not belong to the set of reported candidateCell IDs, the UE determines to use a subframe offset of the currentserving cell for the DMRS scrambling in step 1130.

The RSRP measurement performed by a UE refers to an intensitymeasurement of a cell-specific Reference Signal (CRS) sent by a cell. Inthe LTE and/or LTE-A system, the RSRP measurement reports are used bythe BS to determine whether to hand over a UE to another cell. The RSRPmeasurement for a cell implies that the UE has received asynchronization signal from the cell and has identified the Cell ID andthe subframe offset of the cell. Therefore, in the exemplary embodimentof FIG. 6, for a given cell, the UE may identify the subframe offset ofthe cell without separate signaling.

As an example for the exemplary embodiment shown in FIG. 6, in a casewhere the UE has sent the BS an RSRP measurement report for two cellshaving Cell ID X and Cell ID Y. In this case, the UE is aware of thesubframe offsets of the cells with Cell ID X and Cell ID Y. Thereafter,when the BS notifies the UE of the Cell ID X through the PDCCH or theE-PDCCH, then the UE may use the subframe offset corresponding to CellID X, which is already known to the UE, in order to determine theinitial state for the DMRS scrambling without additional signaling.

Likewise, when the BS notifies the UE of Cell ID Y through the PDCCH orthe E-PDCCH, then the UE may use the subframe offset corresponding toCell ID Y to determine the initial state for the DMRS scrambling. On theother hand, when the BS notifies the UE of Cell ID Z through the PDCCHor the E-PDCCH, because an RSRP measurement report for a cell with CellID Z has not been sent, the UE uses a subframe offset of the currentserving cell to determine the initial state for the DMRS scrambling.

As described above, the BS provides information on the scramblingsequences to the UE, and generates the DMRS scrambling sequencesaccording to the information and sends the same to the UE. The UEgenerates scrambling sequences based on the received information,performs channel estimation using the generated scrambling sequences andthe received scrambling sequences, and receives data from the BSaccording to the channel estimation result.

FIG. 12 is a block diagram of a data transmission apparatus according toan exemplary embodiment of the present invention.

Referring to FIG. 12, the data transmission apparatus, which may be aneNB and/or a BS, may include a wireless communication unit 1210, acontrol unit 1220, and a storage unit 1230. The wireless communicationunit 1210 may send and receive data and signals to and from UEs withinthe coverage area of the BS. In particular, the wireless communicationunit 1210 may sends information for the DMRS scrambling to a UE undercontrol of the control unit 1220.

The control unit 1220 controls operations to transmit information onmultiple candidate transmission points to a UE through higher layersignaling, and to send information used for determining the initialstate for the DMRS scrambling to the UE through the PDCCH or theE-PDCCH. Furthermore, the control unit 1220 may control overalloperations of the BS and components and elements included in the BS. Thestorage unit 1230 may store information necessary for performing theoperations of the exemplary embodiments of the present invention asdescribed above. For example, the storage unit 1230 may storeinformation as illustrated in Table 1 and Table 2. Furthermore, thestorage unit 1230 may store information, applications, and otherinformation used for the operations of the BS.

FIG. 13 is a block diagram of a data reception apparatus according to anexemplary embodiment of the present invention.

Referring to FIG. 13, the data reception apparatus, which may be a UE,may include a wireless communication unit 1310, a control unit 1320, asequence generation unit 1330, and a storage unit 1340. The wirelesscommunication unit 1310 may receive data from a BS via multipletransmission points and may receive information used for data reception.For example, the wireless communication unit 1310 may receive multiplecandidate values usable for DMRS scrambling and may receive anindication to or a notification of a candidate value to be used fordetermining the initial state from the BS under control of the controlunit 1320.

The control unit 1320 may control the wireless communication unit 1310to receive information used for generating the DMRS scrambling sequencesfrom a BS. For example, the control unit 1320 may control an operationto receive candidate sets of data through higher layer signaling and toreceive an indication to or a notification of a candidate set to be usedfor determining the initial state through the PDCCH or the E-PDCCH.Furthermore, the control unit 1320 may control overall operations of theUE.

The sequence generation unit 1330 may determine the initial state forthe DMRS scrambling sequences using candidate values received from theBS. When a subframe offset is not received from the BS, the sequencegeneration unit 1330 determines a subframe offset according to the CellID and a set of candidate Cell IDs that have been reported to the BS asa result of an RSRP measurement.

The storage unit 1340 may store information necessary for generating theDMRS scrambling sequences. For example, the storage unit 1340 may storeinformation on candidate sets received from the BS and information on aset of candidate Cell IDs reported to the BS. Furthermore, the storageunit 1340 may store information on applications, user data, and otherinformation used by or generated during operations of the UE.

According to the exemplary embodiments of the present invention, themethod and apparatus for data transmission in a network supporting CoMPtransmission may effectively randomize signal interference when multiplecells send data to one UE through CoMP transmission by having the cellsto perform different DMRS scrambling operations.

The meaning of specific terms or words used in the specification and theclaims should be construed in accordance with the spirit of theinvention without limiting the subject matter thereof The description ofthe various exemplary embodiments is to be construed as exemplary onlyand does not describe every possible instance of the invention.Therefore, it should be understood that various changes may be made andequivalents may be substituted for elements of the invention.

While the invention has been described with reference to certainexemplary embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims and their equivalents.

What is claimed is:
 1. A data transmission method for a Base Station(BS) capable of sending data to a User Equipment (UE) through multipletransmission points, the method comprising: transmitting candidate setsof initial state information used to generate Demodulation ReferenceSignal (DMRS) scrambling sequences for the transmission points to theUE; and transmitting an indication corresponding to at least onecandidate set of initial state information respectively associated withat least one transmission point to the UE, wherein the initial stateinformation is used by the UE to generate the DMRS scrambling sequences.2. The data transmission method of claim 1, wherein the initial stateinformation comprises a cell identifier, a subframe offset and ascrambling index corresponding to a transmission point.
 3. The datatransmission method of claim 1, wherein the initial state informationcomprises a cell identifier and a scrambling index corresponding to atransmission point.
 4. The data transmission method of claim 1, whereinthe at least one candidate set of initial state information is sent tothe UE through higher layer signaling, and wherein the indicationcorresponding to the at least one candidate set of initial stateinformation respectively associated with a determined transmission pointis sent to the UE through a Physical Downlink Control Channel (PDCCH) oran Enhanced-PDCCH (E-PDCCH).
 5. The data transmission method of claim 1,wherein each of the at least one candidate set of initial stateinformation is composed of multiple pieces of data and is transmitted asa group of the multiple pieces of data to the UE, and wherein theindication corresponding to the at least one candidate set of initialstate information respectively associated with a transmission point forwhich the user equipment is determined to generate the DMRS scramblingsequences is transmitted to the UE.
 6. A data reception method for aUser Equipment (UE) capable of receiving data from a Base Station (BS)through multiple transmission points, the method comprising: receiving,from the BS, candidate sets of initial state information used togenerate Demodulation Reference Signal (DMRS) scrambling sequences forthe multiple transmission points; receiving, from the BS, an indicationcorresponding to a candidate set of initial state information associatedwith a transmission point determined in order to generate the DMRSscrambling sequences; determining an initial state for generating theDMRS scrambling sequences according to the indicated candidate set ofinitial state information; and generating the DMRS scrambling sequencesaccording to the determined initial state.
 7. The data reception methodof claim 6, wherein the initial state information comprises a cellidentifier, a subframe offset and a scrambling index corresponding to atransmission point.
 8. The data reception method of claim 6, wherein theinitial state information comprises a cell identifier and a scramblingindex corresponding to a transmission point.
 9. The data receptionmethod of claim 8, wherein the determining the initial state comprises:identifying a subframe offset using a cell identifier included in theindicated candidate set; and determining the initial state according tothe identified subframe offset, a cell identifier and a scrambling indexincluded in the indicated candidate set.
 10. The data reception methodof claim 9, wherein the identifying the subframe offset comprises:determining whether the cell identifier included in the indicatedcandidate set is contained in an RSRP measurement report that was sentto the BS; and determining to use a subframe offset associated with thecell identifier included in the indicated candidate set for determiningthe initial state when the indicated cell identifier is contained in theRSRP measurement report; and determining to use a subframe offsetassociated with a cell identifier of the current serving cell fordetermining the initial state when the indicated cell identifier is notcontained in the RSRP measurement report.
 11. The data reception methodof claim 6, wherein the candidate sets of initial state information arereceived from the BS through higher layer signaling, and wherein theindication corresponding to a candidate set associated with a determinedtransmission point is received from the BS through a Physical DownlinkControl Channel (PDCCH) or an Enhanced-PDCCH (E-PDCCH).
 12. The datareception method of claim 6, wherein each candidate set of initial stateinformation is composed of multiple pieces of data and is received as agroup of the multiple pieces of data from the BW, and wherein anindication corresponding to a candidate set associated with atransmission point for which the user equipment is determined togenerate the DMRS scrambling sequences is received from the BS.
 13. Adata transmission apparatus comprising: a wireless communication unitfor sending data to a User Equipment (UE) through multiple transmissionpoints; and a control unit for controlling a process of transmitting, tothe UE, candidate sets of initial state information used to generateDMRS scrambling sequences for the transmission points, and fortransmitting an indication corresponding to at least one candidate setof initial state information respectively associated with at least onetransmission point to the UE, wherein the initial state information isused by the UE to generate the Demodulation Reference Signal (DMRS)scrambling sequences.
 14. The data transmission apparatus of claim 13,wherein the control unit controls an operation to send the at least onecandidate set of initial state information to the UE through higherlayer signaling and to send the indication corresponding to a candidateset of initial state information respectively associated with adetermined transmission point to the UE through a Physical DownlinkControl Channel (PDCCH) or an Enhanced-PDCCH (E-PDCCH).
 15. A datareception apparatus comprising: a wireless communication unit forreceiving data from a Base Station (BS) through multiple transmissionpoints; a control unit for controlling a process of receiving, from theBS, candidate sets of initial state information used to generateDemodulation Reference Signal (DMRS) scrambling sequences for themultiple transmission points, and for receiving, from the BS, anindication corresponding to a candidate set of initial state informationassociated with a transmission point determined in order to generate theDMRS scrambling sequences; and a sequence generation unit fordetermining an initial state for generating the DMRS scramblingsequences according to the indicated candidate set of initial stateinformation, and for generating the DMRS scrambling sequences accordingto the determined initial state.
 16. The data reception apparatus ofclaim 15, wherein the initial state information comprises a cellidentifier, a subframe offset and a scrambling index corresponding to atransmission point.
 17. The data reception apparatus of claim 15,wherein the initial state information comprises a cell identifier and ascrambling index corresponding to a transmission point.
 18. The datareception apparatus of claim 17, wherein the sequence generation unitidentifies a subframe offset using a cell identifier included in theindicated candidate set, and determines the initial state according tothe identified subframe offset, a cell identifier and a scrambling indexincluded in the indicated candidate set.
 19. The data receptionapparatus of claim 18, wherein the sequence generation unit determineswhether the cell identifier included in the indicated candidate set iscontained in an RSRP measurement report that was sent to the BS, whereinthe sequence generator determines to use a subframe offset associatedwith the cell identifier included in the indicated candidate set fordetermining the initial state when the indicated cell identifier iscontained in the RSRP measurement report, and wherein the sequencegenerator determines to use a subframe offset associated with a cellidentifier of the current serving cell for determining the initial statewhen the indicated cell identifier is not contained in the RSRPmeasurement report.
 20. The data reception apparatus of claim 15,wherein the control unit controls an operation to receive, from the BS,multiple candidate sets of initial state information composed ofmultiple pieces of data such that each candidate set is a group, andwherein the control unit controls an operation to receive, from the BS,an indication corresponding to a candidate set of initial stateinformation respectively associated with a transmission point determinedto generate the DMRS scrambling sequences.